Read only optical disks such as CD-ROM and DVD-ROM are used to disseminate software, audio, and recently, motion imaging. With each of these information types there have been concerns of illegal copying of the information. The recording industry has used various methods of data identification, data authentication, and data encryption to facilitate the prevention of illegal copying.
There is a generic problem of determining if the information on an optical disk has been previously accessed. Often, the first access to information is to be treated differently than subsequent accesses. To determine if a particular disk has been previously accessed, information must be recorded on the disk during the first access to indicate that a previous access has occurred. This is not possible on a ROM disk such as an audio CD. Furthermore, devices which only read optical disks, such as CD-ROM drives, DVD-ROM drives, or CD, DVD, and LD (Laser Disk) Video Players do not have the capability to drive the laser to a sufficiently high power to mark an optical disk, nor to modulate the laser power, which is the method used to record information on the optical disk.